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**Type I and Type II Errors - Making Mistakes in the Justice System

This webpage uses the criminal trials in the US Justice system to illustrate hypothesis testing, type I error, and type II error. An applet allows the user to examine the probability of type I errors and type II errors under various conditions. An applet allows users to visualize p-values and the power of a test. Keywords: type I error, type II error, type one error, type two error, type 1 error, type 2 error
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Content Quality Concerns: 
1. The text description here sometimes discusses an error and the probability of an error interchangably. These are distinct concepts, and the instructor needs to help students understand this. 2. The authors incorrectly state that alpha is "equal to the p-value." Most statisticians would agree that alpha is the significance level. 3. The authors don't make it explicit that alpha and beta are inversely related only if the amount of information is assumed constant. In fact, if more information is gathered, then it is possible to reduce both probabilities because the relevant sampling distributions become less variable. 4. The false notion that researchers always want to evaluate the alternative hypothesis is perpetuated. 5. In this applet only greater than alternatives are allowed. The instructor should be sure to explain to students that other alternatives are available.
Content Quality Strengths: 
The text illustration of this item is nicely written and fun to read. It uses an easily understood analogy of a criminal trial. Additionally, the applet is very helpful for understanding the relationship between Type I and Type II errors. This is done by allowing the user to move the location of the true distribution relative to the distribution under the null hypothesis.
Ease of Use Concerns: 
Ease of Use Strengths: 
Very easy to use. The applet layout is uncluttered and intuitive (no pun with the URL intended).
Potential Effectiveness Concerns: 
The text explanation is quite similar to a textbook explanation. The included applet will need specific questions for the student to help them explore the relationship. The instructor may also want to supplement this applet with connections to real world examples other than the trial analogy.
Potential Effectiveness Strengths: 
The applet is useful for visually and dynamically illustrating the connection between alpha and beta when the amount of information is held constant. The applet could be helpful if a series of guided questions were written to accompany this material, or if the instructor used it in class where he/she could ask the questions and explain.
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Intended User Role: 
Learner, Teacher
Resource Type: 
Free for All
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